Brake



Jan. l1, 1938. E. G. CARROLL Er AL 'BRAKE Filed may 18, 193.2

3 Sheets-Sheet l INVENToRs Euc-rENE G.CARRo\ CEcm H. TAYLOR BY M4, ATTORNEY Jan. 11, 19348. E G, CARROLL Er AL 2,104,735

BRAKE Filed May 18 193.3 3 Sheets-Sheet 2 INVENroRs 776.2 EUGENE G. CARRoLx.

gyacn. HTAYLOR di frime/7 Jan. 11, 1938. E. G. CARROLL ET'AL 2,104,735

BRAKE Filed May 18, 19343 3 Shee'f's-Shee'l.,` 3

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3 323. cran. H. Tanon ATRNE?g Patented Jan. 11, 1938 UNITED STATES BRAKE Eugene G. Carroll and Cecil H. Taylor, South Bend, Ind., assgnors to Bendix Aviation vCorporation, South Bend, Ind., a corporation of Delaware Application May 18, 1932, Serial. No. 612,136

16 Claims.

This application relates to braking systems and is disclosed'as embodied in'a hydraulic braking system.

In brake apparatus it is necessary to provide certain clearances between the friction elements in lorder to prevent dragging of the brakes. These clearances are increased in operation through wear of the parts. The maximum a1- lowable travel of a brake pedal (such as usually is used in operating brakes) is limited by space in the vehicle and by the necessity of comfortable operation by the driver. Due to these factors the possible leverages have usually heretofore been limited to a degree sometimes considered uncle sirable. y

It has been proposed to provide two phase systems in which part of the brake operating stroke is accomplished by a relatively large low pressure piston at relatively low leverages and part of the stroke is accomplished by a relatively small high pressure piston at relatively high leverages. Some of the prior art proposed designs include a spring operated valve through which liquid is by-passed from in front vof a low.

pressure piston during the high pressure phase of the operation. Heretofore these valves have been controlled by the pressure of liquid which acts upon the low pressure piston and therefore the full force of the spring has reacted upon the pedal so that the results obtained have not been as advantageous as could be desired.

One of the objects of this invention is to provide a two phase system of hydraulic brakes in which a pressure relief valve is controlled by the pressure developed by the high pressure piston.

A further object of the invention is to provide improved means for lubricating the packing cups of a hydraulic brake system.

A feature of the invention is the location of a controlling valve within an operating piston.

A further feature of the invention is the provision of a recess in the wheel cylinder for supplying liquid to ythe outside lof cups which are to be lubricated.

A further feature of the invention is an anchor provided with a cam surface and shiftable in response to drum'expansion and contraction so that the released positions of the Shoes correspond substantially to the condition of the drum with which they cooperate.

Further features and objects of the invention will be apparent from a reading of the subjoined specification and claims and after consideration of the accompanying drawings in which;

ied form-of wheel cylinder;

Figure 6 is a view in section taken substantially on the line 6-6 of Figure 5;

Figure '7 is a view partly in section and partly diagrammatic illustrating a further modiiication; l5

Figure 8 is a fragmentary View showing the position of the large piston by-pass valve of Figure 1 in its operated position; and

Figure 9 is avfragmentary view showing the large piston by-pass valve of Figure 4 in its oper- 20 ated position. l

Referring in detail'to Figure 1 we have shown a brake drum Ill provided with a backing plate l2 on which there are' pivotally mounted as on anchors I4 and I6 a pair of brake shoes I8 and 25 20. Interposed between the free ends of the shoes is a wheel cylinder 22 adapted to move the shoes I8 and 2U into and out of contact with the drum I0 by means of links 24 and 26 pivotally connected to the shoes and bearing upon the pis- 30 tons 28 and, 30. A return spring 3| serves to release the shoes from contact with the. drum when they are not forced into contact therewith by the Wheel cylinder.

A master cylinder 32 supplies liquid under pres- 35 sure to the wheel cylinder 22 by means of a cnnduit 33. The master cylinder 32 comprises a cylindrical casting 34, a cap 36 for the outer end thereof, a reservoir 38 formed integrally with the casting 34 and a plunger 40. The cylinder is pro- 40 vided with an annular head 42 with which there is associated an annular packing cup 44 maintained in the desired position, by means of a slotted tube 46. The casting 34 is provided with a restricted inlet port 48 and a relatively large 45 opening 50 both of which are at times adapted to allow the passage of liquid in eitherdirection between the reservoir 38 and the cylinder 34.

The plunger 40 comprises a rearward piston 52 50 equipped With an annular packing cup 54 which serves to maintain a liquid seal behind a`main piston 56 and which may therefore be termed a sealing piston. The piston 56 is provided with an annular cup 58 and normally is positioned 55 just rearwardly of the port 40, so that it covers the opening 50. The piston 56 is adapted to forceliquid to the brakes during the low pressure phase of operation but not during the high pressure phase of operation and therefore may be termed a low pressure piston. The plunger 40 is formed adjacent its forward end with an extension 60 of relatively small diameter. This extension passes through the central openings in the annular piston 42 and in the packing cup 44 and throughout both the high pressure and the low pressure phases of operation is adapted to force liquid to the wheel cylinders. It may be therefore termed the high pressure piston. It is provided with ports 62 by which liquid may pass the head 42 and the cup 44 while the system is at rest. Thus the entire system may be compensated for changes in the volume of the fluid due to rises and falls of temperature by means of the ports 48 and 62.

The plunger 40 is formed with a central passageway within which there is positioned a valve member 64. 'I'his valve member is provided at its forward end with a packing cup 66 on which the liquid pressure ahead of the piston 60 acts at all times. The valve member is normally maintained in its forward position by means of a spring 68. It is provided with spaced ports 10 and 12 and passes through a sealing cup 15. Thus in its normal position shown it prevents the passage of fluid from in front of the piston 56 to the rear thereof. However, when pressure ahead of the high pressure piston 60 is raised suiiiciently to overcome the spring 68 and the valve member 64 is thus moved rearwardly, liquid may be bypassed from in front of the piston 56 through the ports 10 and the ports 12 and through ports 13 to the rear of the piston 56 whence it may communicate with the reservoir 38. It is to be understood that pressure on the front of the piston 64 moves it rearwardly lso that while the ports 10 remain in front of the packing 'I5 the ports 12 are moved rearwardly of said packing and register with grooves 43a in head 43 and are connected by said grooves 43a with grooves 43h also formed in said head 43.

'I'he structure of the wheel cylinder 22 is disclosed more clearly in Figure 2. The cylinder comprises a cylindrical casting 16 formed with a substantially uniform bore 18 in which there are positioned pistons 28 and 30. Each of these pistons has an inwardly extending projection such as the projections 84 and 86 which contact with each other to limit the inward movement of the pistons. Each is provided with an annular collar such as 88 and 90 and with operating annular cups such as thevcups 92 and 94 which are positioned inward of the collars 88 and 90. Outward from the collars 88 and 90, the pistons are provided with sealing cups 96 and 98 which are spaced from the blocks 88 and 90 by means of slotted guide rings |00 and |02. Thus there is provided between the cup 96 and the collar 88 and between the cup 98 and the collar 90 a pair of recesses adapted to contain liquid to provide a liquid seal for the cups 92 and 94 and to insure the proper lubrication of the cups 92 and 94 which have to withstand the high pressures developed by the improved master cylinder disclosed. Communicating with the sealing recesses by means of ports |03 and |05 there is provided in the casting 16 a relatively large recess |04 which is adapted at times to communicate with the bore 18 but is normally sealed therefrom by means of a conical valve formed by a plug |06 having its inner end seated in a. port |01. Tapped openings |08 are normally closed by plugs |09 but may be opened for bleeding the system.4

In the operation of a braking system constructed according to the above description operation of the master cylinder -through a pedal connected to the piston rod 14 moves the plunger 40 forward and through the piston 56 and the piston 60 forces a large quantity of iiuid to the wheel cylinders, liquid being forced past the sealing cup 44 by the piston 56 by deflecting the cup 44.

.As soon assubstantial resistance to movement of the wheel cylinders is encountered the pressure in the system increases thus forcing back the valve member and allowing the liquid just ahead of the piston 56 to by-pass back to the reservoir. Thereafter the brakes are operated through movement of the high pressure piston 60 at consequent smaller eifort on the part of the operator.

'I'he master cylinder shown in Figure 3 comprises a cylinder proper |34, a reservoir |38, a relief chamber |15 and a plunger |40. The plunger |40 includes a sealing piston |52, a `low pressure piston |56, a high pressure piston |60, the latter being adapted to pass through an annular head |42. Intermediate the normal position of the piston |56 and the head |42, the cylinder is provided with a pair of ports I 11 and |19 which communicate with the interior of the pressure relief chamber |15. Within the pressure relief chamber there is provided a plunger |8| normally maintained in its upper position by a spring |83 and provided with an annular sealing cup |85.

The head |42 has a projecting rim which fits loosely in a groove |3411 formed between the front end of the cylinder |34 and the cap |34b screwed thereon. The cylinder |34 is provided with a bore |34e normally sealed by plug |34d, the plug being removed during the bleeding operation.

The head 42 is provided with grooves |42a, |4217, and |42c, and with port |42d which allow liquid to pass forward past said head at all times by deflecting the sealing cup |42e. The piston |60 is formed witha central bore |60a and with intersecting ports |60b adapted to register with grooves |42a and |42b and with port |42d. By means of said ports and grooves and bore, liquid may pass rearwardly of the head |42 when the parts are in the released position as shown.

The head |56 is provided with grooves |56a by means of which liquid may pass forwardly past said head at all times byv deflecting the sealing cup |58.

'Ihe cylinder |34 is further provided with ports |34e and |34f which connect it with the reservoir |38. The port |34e is covered by a valve |38a resiliently held on its seat by a light spring |3817.l

It may be seen that in the operation of the brake, the piston |56 and thev head |42 form a pump for drawing liquid from thereservoir |38 through the port |34f and the bores |56a and past the sealing cup |58. Thence the liquid is forced past the head |42. When the parts are in the released position as shown, pressure of the wheel cylinder springs acting on the liquid in the system is effective to lift the spring |3812 and allow the escape of excess liquid. However, the liquid in the system is kept under a slight pressure because of the spring |38b and the sucking in of air into the system is prevented. 1

In the operation of this form of master cylinder, the piston rod |14 is moved by means of a pedal through the lever I 81 and forces the plunger |40 forward and thus forces fluid to the brakes 75 by means of both the low pressure piston |58 and the high pressure piston |68. As soon as the port |19 is passed by the cup |58, liquid is able to by-pass from in front of the piston |56 to the rear thereof. Should the pressure ahead of the low pressure piston |56 become too great before the piston |56 has passed the bore |18 the spring |83 will compress and allow the fluid to pass into the pressure relief chamberv| through either the port |11 or theport |19.

In Figure 7 we have shown a master cylinder arrangement similar to that shown in Figure 3. 'I'he master cylinder proper is provided with a port 411 which is connected by a conduit 415 provided with a valve 485 positioned conveniently for the operation by the driver. Beyond the valve 485 the conduit 415 loads back to the reservoir 438. As may be seen the valve 485 is normally held closed. In normal braking the pres- ,sure is developed by both pistons acting in combination. However, should it be desired to apply the brakes more rmly than usual, the pedal is depressed until substantial resistance is encountered, then the valve 485 is opened so as to relieve the pressures developed by the large piston and thereafter relativelyhigh pressures are developed by the small piston alone.

The master cylinder 232 shown in Figure 4 is in most respects similar to the cylinder shown in Figure l. However, the plunger 248 is simpler in design inasmuch as it comprises a rod having substantially a uniform diameter throughout and having the piston 258 slidably mounted thereon and held against rearward movement by means of a shoulder on the rod. Instead of a single cup through which the valve member passes for sealing it, the valve member 264 is provided with a pair af cups 213 and 215 which slide through the hollow plunger 248. 'I'he valve member is provided with intersecting bores 211, 219 and 28|, the former of which is adapted at times to register with a port 283 in the plunger 248 and the latter of which is adapted at times to communicate with ports 285 in said plunger.

The annular head 242 like the head |42 is loosely fitted in a groove 234a formed between the cylinder 232 and the cap 234. The cylinder is provided with a threaded bore -232a normally closed by a plug 232b. the bore being provided so that the cylinder maybe bled. The vhead 242 is provided with bores and grooves (not shown) leading to the rear of the sealing cup 242e and to the ports 268a formed in the forward end 26|) of the plunger 248. Said ports in the head 242 correspond in design and function to the bores and grooves ifi2a, |42b, |620, and |42d. Ports 234e and 238! connect the cylinder 232 with the reservoir 238. The port 234e is covered by a valve member 238:1 reslliently held on its seat by the spring 23817. The valve member 2380. is hollow and is arranged to trap air therein so that the liquid in the system may be maintained under pneumatic pressure. The pressure is developed by a pumping action similar to that previously described in connectionv with Figure 3.

The piston 255 is provided with bores 256a so that liquid may at any time flow forward past the piston compressing the cup 258.

In the operation of this embodiment pressure on the pedal forces the plunger 248 forward carrying with it the piston 256. This forces a relatively large volume of liquid forward tothe brakes, part being displaced by the forward end 268 of the plunger 248 and part being displaced by the piston 256, the latter portion being forced past the head 242 and the sealing cup 242e defiecting the latter. As soon as the pressure developed is strong enough the piston 264 is moved "l mediate the sealing cups 213 and 215 there is less possibility of leakage.

In Figures 5 and 6 we have shown a brake drum 3|8 having a backing plate 3|2 and adapted to cooperate with brake shoes 3|8 and 328. The shoes 3|8 and 328 instead of being anchored on the backing plate,` are secured to each other at their opposite ends. The shoes 3|8 and 328 have secured thereto links 324 and 328 by means of which the shoes are loperated and through which the shoes anchor. The shoes are floating and both anchor in one direction of drum rotation through oneiink andV in-the other direction of drum rotation through the other link. Secured to the backing plate 3|2 is a wheel cylinder 322 `provided with a piston 388 associated with a piston rod 38|. The outer end of the piston rod 38| passes through the backing plate 3|2 and contacts 'with a small lever 3831 pivoted upon a larger lever 385Which is itself pivoted upon a clamp secured to the backing plate. A lever 381 similar to the lever 385 but reversed thereto is pivoted upon a similar lclamp secured to the backing plate 3|2 and is adapted to be operated by the lever 383. The levers 385 and 381' anchor upon a slidablei pin 389. They are adapted to be operated by the piston 388 through the piston rod 38| and are adapted, to move the shoes into contact with they drum. The pin 389 is slidably mounted in bearings 39| and 893 and is provided adjacent its outer end with a roller 395 which contacts with the rim of the'drurn. A spring 381 maintains the roller 395 in contact with the drum and thus the position of the pin is determined by the drum and the pin therefore moves with th'e expansion and contraction of the drum. The inner end of the pin is formed .with a conical surface 391 upon .which the levers 385 and 381 are adapted tov anchor. The cylinder- 322 is provided with bores 323 and 323a to which are connected conduits (not shown) similar to the conduit 33 of Figure l. Liquid may be forced by a master cylinder through Asaid conf duits into the cylinder 322 tb' displace the piston 388 to apply the brake.

lin the operation of this wheel cylinder liquid supplied to the cylinder forces the piston rod 38| outward andl thus tends to rotate the levers 385 and 381 equally. Due to the wiping action when the brake is applied, the torque of the brake application reacts through one of the levers in one direction of drum rotation and through the other lever in the other direction of drum rotation. It

thus reacts through one or the other of the levers piston always returns to its normal position so that regardless of the expansion of contraction of the drum, the pedal travel remains uniform.

It is to be understood that the above described embodiments of the invention are for the purpose of illustration only and various changes may be made therein without departing from the spirit and scope of the invention.

We claim:

1. In a hydraulic brake system, a. cylinder; an annular piston slidable therein; a concentric piston of smaller diameter extending forward from said annular piston and formed with a longitudinal bore extending to the front end thereof and with a port communicating with' said bore: a valve member slidably mounted in said bore and extending rearwardly through said annular piston, said valve member being formed with a longitudinal bore extending through a part of its length and with a pair of intersecting bores, one adapted to register with said port and the other adapted to communicate at times with the portion of said cylinder rearwardly of said annular piston; a spring acting on said valve and normally maintaining said intersecting bores out of communication with said rearward chamber; an annular head through which the front end of said small area piston slides, and a packing cup associated with the front end of said valve member whereby fluid pressure in advance of said head acts on said valve to move it to open communication between the portion of the cylinder just in advance of said annular piston and the portion rearwardly thereof.

2. In a hydraulic brake system, a cylinder, a piston in said cylinder having a recess formed therein and having transverse ports, a slidable valve element in said recess formed with a longitudinal bore and a plurality of intersecting transverse bores adapted at times to register with said transverse ports, and a pair of reversed cups positioned between said transverse bores.

3. In a fluid system for operating brakes, a

master cylinder, a piston having a relatively large diameter associated therewith, a piston having a relatively small diameter connected with the large diameter piston and comprising a forward exten- Sion thereof and having a recess formed therein at its forward end, means for conducting uid acted on by both of said pistons to said brakes, and a slidable valve element in said recess effective' attimes to by-pass liquid from the front to the rear of said large diameter piston and controlled by the pressure ahead of said small diameter piston.

4. In a fluid system for operating brakes, a master cylinder, a piston having a relatively large diameter associated therewith, a piston having a' relatively small diameter connected with the large diameter piston and comprising a forward extension thereof and having a recess formed therein at its forward end, means for conducting fluid acted on by both of said pistons to said brakes, a slidable valve element in said recess effective at times to by-pass liquid from the front to the rear of said large diameter piston and controlled by the pressure ahead of said small diameter piston, and means comprising an annular head through which the small diameter piston passes for preventing fluid pressure developed by the small diameter piston from reacting on said large diameter piston.

5. In a fluid system for operating brakes; a master cylinder; a piston having a relatively large diameter associated therewith, a pair. of

aromas relatively movable piston elements associated with said large diameter piston one of which is formed as amsleeve having a diameter smaller than that of the large diameter piston and the other piston element being cylindrical, fitting within the sleeve element, being formed with a longitudinal bore and a plurality of intersecting transverse bores, and serving together with said sleeve element to form a valve for by-passing liquid from in front of said large diameter piston to the rear of said large diameter piston and one of the piston elements being connected with the large diameter piston and comprising a forward extension thereof, and the element not connected to said large diameter piston being controlled in its relative movement by the pressure of the liquid ahead of said piston element; and means for conducting fluid acted on by both oi said pistons to said brakes.

6. In a fluid system for operating brakes, a master cylinder, a piston having a relatively large diameter associated therewith, a pair of relatively movable piston elements associated with said large diameter piston one of which is formed as a sleeve having a diameter smaller than that ofthe large diameter piston and the other piston element being cylindrical, fitting within the sleeve element, being formed with a longitudinal bore and a plurality of intersecting transverse bores and serving together with said sleeve element to-form a valve for by-passing liquid from in front of said large diameter piston to' the rear of said large diameter piston andv one of the piston elements being connected with the large diameter piston and comprising a forward extension thereof, and the element not connected to said large diameter piston being controlled by the pressure of the liquid ahead of said piston element; means for conducting fluid acted on by both of said pistons to said brakes; and means comprising an annular head through which the small diameter piston passes for preventing fluid pressure developed by said small diameter piston from reacting on said large diameter piston. v

7. In a hydraulic brake system, a cylinder, a piston in said cylinder having a recess formed therein and having transverse ports connected to said recess, a slidable valve element in said recess formed with a longitudinal bore and a piurality of longitudinally spaced intersecting transverse bores adapted at times to cooperate with said transverse ports to allow the escape of liquid from in front of said piston to the rear of said piston, and a sealing cup at times positioned between said transverse bores.

8. In a hydraulic brake system, a cylinder, a piston in said cylinder having a recess formed therein and having a transverse port, a slidable vvalve element in said recess formed with a longitudinal bore and with an intersecting transverse bore adapted at times to cooperate with said transverse port to conduct liquid from said transverse port, and a sealing cup arranged to prevent the passage of liquid through said recess except by way of said transverse port and said transverse longitudinal bore.

9. In a hydraulic brake system, a cylinder, a piston in said cylinder having a relatively large diameter, a relatively small diameter piston in said cylinder having a recess formed therein and having a transverse port, and a slidable valve element in said recess formed with a longitudinal bore and with a plurality of intersecting transverse bores one of which is adapted at 75 times to cooperate with said transverse port to conduct liquid from ahead of said large diameter piston to said longitudinal bore and the other of which is adapted to conduct liquid from said longitudinal bore to the rear of said large diameter piston.

10. In a hydraulic brake system, a cylinder, a piston in said cylinder having a relatively large diameter, a relatively small diameter piston in said cylinder lhaving a recess formed therein and having a transverse port, a slidable valve element in said recess formed with a longitudinal bore and with a plurality of intersecting transverse bores one of which is adapted at times to cooperate with said transverse port to conduct liquid from ahead of said large diameter piston to said longitudinal bore and the other of which is adapted to conduct liquid from said longitudinal bore to the rear of said large diameter piston, and means for controlling the position of said slidable valve element depending on the pressure of the liquid ahead of said small diameter piston.

11. In a hydraulic brake system, a cylinder, a piston in said cylinder having a relatively large diameter, a relatively small diameter piston in said cylinder having a recess formed therein and having a transverse port, a slidable valve element in said recess formed with a longitudinal bore and with a plurality of intersecting transverse bores one of which is adapted at times to cooperate with said transverse port to conduct liquid from ahead of said large diameter piston to said longitudinal bore and the other of which is adapted to conduct liquid from said longitudinal bore to the rear of said large diameter piston, and a sealing cup associated with said small diameter piston and said slidable valve element to prevent the passage of liquid rearwardly between said piston and said valve element except by way of said longitudinal bore.

12. In a fluid system for operating brakes, a master cylinder, a piston having a relatively large diameter associated therewith, a piston having a relatively small diameter connected with the large diameter piston and comprising a forward extension thereof and formed with a recess and with a transverse port, a pressure piston positioned in said recess formed with a longitudinal bore and with a pair of intersecting transverse bores, and means for controlling thev position of said pressure piston depending upon the pressure of the liquid ahead of said smaller piston.

13. In a fluid system for operating brakes, a master cylinder, a piston having a relatively large diameter associated therewith, a piston having a relatively small diameter connected with the large diameter piston, comprising a forward extension thereof and formed with a recess and with a transverse port, a pressure piston positioned in said recess formed with a longitudinal bore and with a pair oi intersecting transverse bores, means for controlling the position of said pres- Sure piston to control the escape of liquid from in front of said large diameter piston to the rear thereof depending upon the pressure of the liquid ahead of said smaller piston, and means to limit the movement of said pressure piston.

14. In a iluid system for operating brakes. a master cylinder, a piston having a relatively large diameter associated therewith, a piston having a relatively small diameter connected with the.

ameter piston, and means comprising an annular head through which the small diameter piston passes for preventing the escape of iluid from in front of the small diameter piston to the rear thereof.

15. In a fluid system for operating brakes, a master cylinder,' a piston having a relatively large diameter associated therewith, a pair of relatively movable piston elements associated with said large diameter piston one of which is formed as a sleeve having a diameter smaller than that of the large diameter piston and the other piston element being cylindrical, fitting within the sleeve element, being formed with a longitudinal bore and a plurality of intersecting transverse bores and serving together with said sleeve element to form a valve for by-passing liquid at times from in front of said large diameter piston to the rear of said large diameter piston and one of the piston elements being connected with the large diameter piston and comprising a forward extension thereof, and the element not connected to said large diameter piston being controlled by the pressure of the liquid ahead of said piston element; means for conducting fluid acted on by both of said pistons to said brakes; and means comprising an annular head through which the small diameter piston passes for preventing the escape of fluid from in front of the small diameter piston to the rear thereof.

16. In a hydraulic brake system, a cylinder, a piston in said cylinder having a relatively large diameter, a relatively small diameter piston in said cylinder having a recess formed therein and having a transverse port, a slidable valve element in said recess formed with a longitudinal bore and with a plurality of intersecting transverse bores one of which is adapted at'times to cooperate with said transverse port to conduct liquid from ahead of said large diameter piston to said longitudinal bore and the other of which is adapted to conduct liquid from said longitudinal bore to the rear of said large diameter piston, and means to control the relative position of said valve element to allow or prevent the conduction of liquid.

EUGENE G. CARROLL. CECIL H. TAYLOR. 

